Author Topic: Put a water tank atop the tower?  (Read 8058 times)

Offline DanClemmensen

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Put a water tank atop the tower?
« on: 05/21/2023 08:15 pm »
I started a new topic because this discussion is cluttering up the base discussion.  Moderators, feel free to move the earlier posts here.

The deluge system will apparently be pressurized by high-pressure gas to a pressure of about 12 bar at the orifices. This is a "head" of about 400 feet. To get the equivalent using a water tower, you need a tower about 400 feet high positioned near the OLM.

But wait! SpaceX already has a 400-ft tower near the OLM. Why not just just put a big water tank at the top? It should be cheaper to operate and probably cheaper to build than the gas pressurization system. You need the same amount of energy to pump the water as you need to compress the gas, but pumping water up to load the tank is almost certainly much cheaper and is logistically simpler. You probably need a pipe less than 1 m in diameter to do the deluge, and the bottom sections of that pipe must handle the entire 12 bar. A smaller pipe can be used to pump the water up, and pumping water up 400 feet is routine.

How would you get said water tank up there?
With a crane. That's how they got all the other stuff up there. If you don't want to rent the super-big Leibart, then erect a small hoist on the top of the tower. Use multiple smaller tanks as they are doing on the ground now. You can also build it in place. For future towers, plan a single larger tank as part of the initial build. Note that big water tanks are a well-understood technology. The bottom of a 33-foot tall tank on top of the tower is only at 2 bar, not at the 12 bar of the pressurized tanks on the ground.
I'd bet that just the cost of the crane mob/de-mob to place the equipment that far up the tower far exceeds the cost of the air pressurization system that they are building.
I suspect that adding a water tank to the existing tower would have been cheaper. You only use a huge crane if you happen to have it on site already. Building a big 2 bar water tank is a well-understood task and happens in towns and cities all over the country all the time. Build it in place, don't build it on the ground and then lift it.

However, I was thinking more about new installation and less about retrofits at BC or KSC. If you are already building the tower, then the tank is just another part of the job and uses the same crew and equipment. In addition to being cheaper and simpler to build and operate, it also has a much smaller incremental footprint (nearly zero). It consumes only water (which can be piped in) and electricity, so much simpler logistics.

Offline alugobi

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Re: Put a water tank atop the tower?
« Reply #1 on: 05/21/2023 08:52 pm »
Why didn't SX do this?

Online joek

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Re: Put a water tank atop the tower?
« Reply #2 on: 05/21/2023 08:53 pm »
Do we know pressure and modulation requirements? That should help inform the solution. Certainly a tall enough water tower can address the pressure issue. Whether that is an optimal solution is another question, also given potential for multiple pads in relatively close proximity. Will leave the rest to our civil-hydraulic experts.

Offline DanClemmensen

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Re: Put a water tank atop the tower?
« Reply #3 on: 05/21/2023 09:22 pm »
Why didn't SX do this?
We don't know when they decided they needed the deluge (or whatever you call it). Retrofitting a water tank may in fact be more hassle than adding the pressurized tanks. In particular the water tank (if feasible at all) may simply take longer to construct, so it may be a cost versus time tradeoff.

There is also the possibility that I have overlooked some major show-stopper. I was paid exactly zero for this idea, and that may be exactly what it's worth.

Offline InterestedEngineer

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Re: Put a water tank atop the tower?
« Reply #4 on: 05/22/2023 02:59 am »
I'm confused.

Why are pressurized tanks a worse solution than some sort of water tower?

Online chopsticks

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Re: Put a water tank atop the tower?
« Reply #5 on: 05/22/2023 03:19 am »
Why didn't SX do this?
Or for that matter, why has no one else done this on any launchpads?

(Or if it has in fact been done, by all means let me know!)
« Last Edit: 05/22/2023 03:21 am by chopsticks »

Offline Lee Jay

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Re: Put a water tank atop the tower?
« Reply #6 on: 05/22/2023 05:24 am »
Why would the tower have been designed to carry an exceptionally heavy tank if they didn't know they were going to need one when it was being designed?

I'm not sure how much water they need but I'm guessing it's measured in hundreds of tons at least.

Pressurized tanks are commonplace. We have five of them where I work.

Offline DanClemmensen

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Re: Put a water tank atop the tower?
« Reply #7 on: 05/22/2023 01:42 pm »
Why didn't SX do this?
Or for that matter, why has no one else done this on any launchpads?

(Or if it has in fact been done, by all means let me know!)
We a see tall water tower at LC-39A, so gravity-fed deluge systems are in use, apparently for Shuttle and for SLS. Integrating it into the launch tower would save cost and footprint, but only when a fixed launch tower is present. Shuttle and SLS used MLPs.

The SpaceX launch tower is already designed for "hundreds of tons" of load. If you don't fill the tank until after you have stacked SS, then the incremental max load may not be too large for an existing tower. The incremental cost of adding it for a new tower is lower than a retrofit.

Offline Coastal Ron

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Re: Put a water tank atop the tower?
« Reply #8 on: 05/22/2023 01:49 pm »
I suspect that adding a water tank to the existing tower would have been cheaper.

However now you are putting even more launch equipment at risk in case there is a launch or capture failure, and it is in a location that is hard to get to, and hard to repair.

The alternative, which is what they are doing today, looks to be far more risk averse, and far more simple to maintain - and it may also cost less overall.
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

Offline edzieba

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Re: Put a water tank atop the tower?
« Reply #9 on: 05/22/2023 01:55 pm »
Pressure discharge systems also have the advantage of being ground-level (ease of maintenance), and of having controllable and variable discharge pressure. A gravity head system has a minimum discharge pressure, and raising the discharge pressure means you'd still need all the pressurised discharge equipment, but it now all needs to be hoisted and worked on at height too.

Since there is no cheap pressurised water supply available on site, and if you'd need to expend energy pumping any water trucked to site up to the top of a water tower, you might as well skip doing that and keep the delivered water at ground level and spend energy pressurising the discharge gas instead (which you can also do with on-site LN2 and a small heater).

Offline aero

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Re: Put a water tank atop the tower?
« Reply #10 on: 05/22/2023 02:45 pm »
What would the pressure head be for a tank on top of the tower? How high is the location for the water tank above the discharge, and would such a tank be a reasonable size for the volume of water needed?
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Offline DanClemmensen

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Re: Put a water tank atop the tower?
« Reply #11 on: 05/22/2023 02:50 pm »
What would the pressure head be for a tank on top of the tower? How high is the location for the water tank above the discharge, and would such a tank be a reasonable size for the volume of water needed?
The estimate made by others on the forum is 12 bar at the nozzles. That requires a 400 foot head at the bottom of the tank on top of the tower. I do not know the required amount of water. You can estimate it by the size of the four pressurized tanks at the BC launch site.

Online abaddon

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Re: Put a water tank atop the tower?
« Reply #12 on: 05/22/2023 03:01 pm »
Pressure discharge systems also have the advantage of being ground-level (ease of maintenance)
This shouldn't be overlooked; imagine the fun every time you have to inspect the tank and instead of a nice ground-level tank you have to go on one of the tallest launch towers in the world that has no built-in infrastructure to get you up there, so you need a massive and expensive crane every time...

IF there is a benefit, it seems very marginal compared with the hassle of getting up there to inspect/repair it.

Offline meekGee

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Re: Put a water tank atop the tower?
« Reply #13 on: 05/22/2023 03:14 pm »
Pressure discharge systems also have the advantage of being ground-level (ease of maintenance)
This shouldn't be overlooked; imagine the fun every time you have to inspect the tank and instead of a nice ground-level tank you have to go on one of the tallest launch towers in the world that has no built-in infrastructure to get you up there, so you need a massive and expensive crane every time...

IF there is a benefit, it seems very marginal compared with the hassle of getting up there to inspect/repair it.
A pressurized gas system will have high pressure initially, and it will drop with time, which is actually what you want as the rocket ascends.

You can get the same effect by fashioning your gravity system as a largish diameter vertical tube-tank, presumably on the back side or just inside the tower.

I'd still favor the gas pressure system though as a minimal-headache solution just because you don't have to invent anything and it works just as well.

If you want to be cool, you could use a Merlin gas generator and turbine set to pump the water in real-time...
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Offline KilroySmith

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Re: Put a water tank atop the tower?
« Reply #14 on: 05/22/2023 03:35 pm »
Pressure discharge systems also have the advantage ... of having controllable and variable discharge pressure.

Step controllable pressure is easily achieved in a gravity-fed system.   Multiple valves of varying sizes will change the effective pressure at the showerhead by moving the pressure restriction to the valve.  So, perhaps a pair of 0.1m valves, a pair of 0.25m valves, a pair of 0.5mm valves, a pair of 1.0m valves.  Turn them on in a binary sequence to change the pressure at the showerhead.  Also provides a lot of redundancy for little cost. 

Offline DanClemmensen

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Re: Put a water tank atop the tower?
« Reply #15 on: 05/22/2023 03:45 pm »
Pressure discharge systems also have the advantage of being ground-level (ease of maintenance)
This shouldn't be overlooked; imagine the fun every time you have to inspect the tank and instead of a nice ground-level tank you have to go on one of the tallest launch towers in the world that has no built-in infrastructure to get you up there, so you need a massive and expensive crane every time...

IF there is a benefit, it seems very marginal compared with the hassle of getting up there to inspect/repair it.
typical municipal water towers are like this, and inspectors just make a long weary climb up the steps. Not the launch tower. The launch tower has an elevator (i.e., "built-in infrastructure"). The top of the hoist for the chopsticks needs inspection more frequently than the water tank would need it.

Online abaddon

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Re: Put a water tank atop the tower?
« Reply #16 on: 05/22/2023 03:52 pm »
Pressure discharge systems also have the advantage of being ground-level (ease of maintenance)
This shouldn't be overlooked; imagine the fun every time you have to inspect the tank and instead of a nice ground-level tank you have to go on one of the tallest launch towers in the world that has no built-in infrastructure to get you up there, so you need a massive and expensive crane every time...

IF there is a benefit, it seems very marginal compared with the hassle of getting up there to inspect/repair it.
typical municipal water towers are like this, and inspectors just make a long weary climb up the steps. Not the launch tower. The launch tower has an elevator (i.e., "built-in infrastructure"). The top of the hoist for the chopsticks needs inspection more frequently than the water tank would need it.
Or, you could not have to do any of that.  I suppose we'll have to wait for SpaceX to build their next tower to know for sure, but if this works out well for them, I imagine they are going to stick with it.

Offline DanClemmensen

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Re: Put a water tank atop the tower?
« Reply #17 on: 05/22/2023 04:01 pm »
Pressure discharge systems also have the advantage of being ground-level (ease of maintenance)
This shouldn't be overlooked; imagine the fun every time you have to inspect the tank and instead of a nice ground-level tank you have to go on one of the tallest launch towers in the world that has no built-in infrastructure to get you up there, so you need a massive and expensive crane every time...

IF there is a benefit, it seems very marginal compared with the hassle of getting up there to inspect/repair it.
typical municipal water towers are like this, and inspectors just make a long weary climb up the steps. Not the launch tower. The launch tower has an elevator (i.e., "built-in infrastructure"). The top of the hoist for the chopsticks needs inspection more frequently than the water tank would need it.
Or, you could not have to do any of that.  I suppose we'll have to wait for SpaceX to build their next tower to know for sure, but if this works out well for them, I imagine they are going to stick with it.
I think so too. However, the whole "stage 0" mantra at SpaceX is about operations costs, and the gravity system would be cheaper, I think.

Offline alexterrell

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Re: Put a water tank atop the tower?
« Reply #18 on: 05/22/2023 04:11 pm »
Rather than a water tank at an altitude of 120m, you could just take a standard wind turbine tower, which is about 5m diameter and 140m high, and seal it.

Very strong, off the shelf solution, and readily available in Texas. Place it just behind the launch tower.

Fill it with water prior to launch and you have a 12 bar solution.

As the water level lowers, the pressure drops. But then the requirements should also drop as the rocket gets a bit further from the pad. Probably the lower half of the tower could be empty, assuming a strong enough bulkhead can be installed.

Offline edzieba

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Re: Put a water tank atop the tower?
« Reply #19 on: 05/22/2023 04:18 pm »
Pressure discharge systems also have the advantage of being ground-level (ease of maintenance)
This shouldn't be overlooked; imagine the fun every time you have to inspect the tank and instead of a nice ground-level tank you have to go on one of the tallest launch towers in the world that has no built-in infrastructure to get you up there, so you need a massive and expensive crane every time...

IF there is a benefit, it seems very marginal compared with the hassle of getting up there to inspect/repair it.
typical municipal water towers are like this, and inspectors just make a long weary climb up the steps. Not the launch tower. The launch tower has an elevator (i.e., "built-in infrastructure"). The top of the hoist for the chopsticks needs inspection more frequently than the water tank would need it.
Or, you could not have to do any of that.  I suppose we'll have to wait for SpaceX to build their next tower to know for sure, but if this works out well for them, I imagine they are going to stick with it.
I think so too. However, the whole "stage 0" mantra at SpaceX is about operations costs, and the gravity system would be cheaper, I think.
It might be cheaper in isolation. But when the launch site already has the hardware for producing and handling high pressure gasses (for the COPVs) any marginal cost advantage probably goes away in favour of commonality.

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